Bronx District Attorney Robert Johnson said yesterday there wasn’t enough evidence to charge a narcotics cop in the fatal shooting of an unarmed man.

Johnson said a three-month investigation found witnesses who confirmed Officer Louis Rivera’s claim that he identified himself as a cop and implored Malcolm Ferguson: “Stop resisting. Why are you resisting?”

Ferguson, 23, a paroled heroin dealer, had six bags of smack in his pocket when Rivera shot him in March, three blocks from the building where Amadou Diallo died.

Ferguson’s father, James Ferguson, called the decision “a great miscarriage of justice.”